Noninvasive assessment of tissue-engineered graft viability by oxygen-17 magnetic resonance spectroscopy

Abstract

Transplantation of macroencapsulated tissue-engineered grafts (TEGs) is being investigated as a treatment for type 1 diabetes, but there is a critical need to measure TEG viability both in vitro and in vivo. Oxygen deficiency is the most critical issue preventing widespread implementation of TEG transplantation and delivery of supplemental oxygen (DSO) has been shown to enhance TEG survival and function in vivo. In this study, we demonstrate the first use of oxygen-17 magnetic resonance spectroscopy ( ¹⁷O-MRS) to measure the oxygen consumption rate (OCR) of TEGs and show that in addition to providing therapeutic benefits to TEGs, DSO with ¹⁷O ₂ can also enable measurements of TEG viability. Macroencapsulated TEGs containing βTC3 murine insulinoma cells were prepared with three fractional viabilities and provided with ¹⁷O ₂. Cellular metabolism of ¹⁷O ₂ into nascent mitochondrial water (H ₂ ¹⁷O) was monitored by ¹⁷O-MRS and, from the measured data, OCR was calculated. For comparison, OCR was simultaneously measured on a separate, but equivalent sample of cells with a well-established stirred microchamber technique. OCR measured by ¹⁷O-MRS agreed well with measurements made in the stirred microchamber device. These studies confirm that ¹⁷O-MRS can quantify TEG viability noninvasively.

Graphical Abstract

Techniques to measure tissue-engineered graft (TEG) viability are limited, but a ¹⁷O-MRS technique is proposed to quantify the viability of macroencapsulated cells. Cells metabolized ¹⁷O ₂ gas into H ₂ ¹⁷O water and this oxygen consumption rate (OCR) was measured with ¹⁷O-MRS. The ¹⁷O-MRS measurements agreed well with those of a stirred microchamber, a well-established technique, and it was found that ¹⁷O-MRS offers a reliable, accurate, and noninvasive approach to TEG viability assessment.